Cathode-ray tube with shielded deflecting plates



Aug. 12, 1947. G. LIEBMANN 2,425,682

CATHODE RAY TUBE WITH SHIELDED DEFLECTING PLATES v Filed Aug. 50, 1944Patented Aug. 12, 1947 CATHODE-RAY TUBE WITH SHIELDED DEFLECTING PLATESGerhard Liebmann, Cambridge, England, assignor to Cathodeon Limited,Cambridge, England,

a British company Application August 30, 1944, Serial'No. 551,863 InGreat Britain August 19, 1943 17 Claims. (Cl. Z50-'458) The inventionrelates to cathode ray tubes, and more particularly to cathode rayoscillograph tubes. In this kind of cathode ray tube an electron beam isformed which throws a small spot on to a suitable screen, which may be auorescent screen or a photographic plate or any other means to registeror record the position, or the position and intensity, of the electronspot. The beam forming this spot is deflected by deflecting plates onwhich suitable potentials are impressed. Usually two sets vof deectingplates are employed, and in many applications of this kind of tube thepotential to be investigated is brought to one set oi plates and analternating potential of a suitable and known Wave form is applied tothe other set of deflecting plates.

If the alternating potentials applied to one or both sets of deflectingplates are of a fairly high frequency, of the order of a megacycle/sec.or more, a serious interaction of the two deilecting potentials becomesapparent owing tothe capacitative coupling between the two sets ofdeilecting plates. An object of the present invention is to eliminatethis fault.

In a cathode ray tube, and particularly a cathode ray oscillograph tube,according to the present invention two or more sets of deflecting platesare entirely enclosed in a shielding metal cylinder of circular or othersuitable cross-section which is adapted to be grounded when the tube isin use, this cylinder being partitioned by metal screening intocompartments entirely shielded from each other, each compartmentcontaining one set of deiiecting plates. Openings of suitable shape andsize have, of course, to be provided in the partitioning screens to letthe electron beam pass through, taking into account the diameter of thelbeam and any deection it may have suffered before passing through theopening. Further openings are provided in the mantle of the shieldingcylinder to allow lead-in wires to the deilecting plates to passthrough. These lead-in wires are sealed through the 'wall of the glassenvelope near the position of the respective deflecting plates.

Preferably, the diameter of the shielding cylinder is only slightlysmaller than the internal diameter of the glass envelope. The envelopeis surrounded near the sealing through position of the deecting plateleads by a metallic screen adapted to be grounded, which, preferably,has a screening flange extending perpendicularly to the axis of the tubeand interposed between the leads from each set of deiiecting plates. Thebottom end of the internal shielding cylinder, facing the cathode end ofthe cathode ray tube, is

constituted lby a metal discor `metal cup, or a combination of both, andmay be shaped and arranged in such a way that it forms the nalaccelerating anode of the cathode ray tube gun` structure, and thuscci-operatesV with the other electrodes in the formation of the electronbeam.

The internal shielding of the cathode ray tube isI completed in a knownway by a metal or graphite or other conductive coating on the inner wallof the tube envelope connected to the nal anode. This conductive coatingmay extend from the bottom end of the internal shielding cylinder to theregistering or recording screen.

The described internal shielding cylinder may:

be used at the same' time as a means for lining up correctly the varioussets of deilecting plates, by assembling the sets of deilecting plates,conveniently with the help of jigs, on suitable insulating annulardiscs, for instance mica discs, which are such as1to engageV theinternal wall of the shielding cylinder when the assembly is placedtherein, thereby correctly locating the sets of deflecting plates.

In order that the invention may be more clearly understood, referencewill `now be made, by way Way of example, to the accompanying drawings,in which v Fig. 1 shows a section through a cathode ray oscillographtube embodying one form of the invention.

Fig. 2 shows a in Fig. 1.

Referring to the drawings, l represents the neck portion of the envelopeof the cathode ray tube which encloses the cathode ray gun and de--ilecting plates and 2 the bulb portion of thetwbe, the front wall 3 ofwhich is coated with fluorescent material 4' to form the viewing screen.Y, The neck portion I accommodates the cathode ray.

gun structure 5 and two pairs of deilecting plates 6 and 1 for 'deectingthe beam in the X andY tedwith the cap Scarrying contact pinsin'knownlmanner. N y A ,Y

According to the `present invention,` the two p Fig. 3 is an externalview of slightly modifiedv tube.

screens II, I2 and I3 to allow the electron beam.

from the cathode gun to pass through. The apertures in the partitioning'screens increase progressively in size from the screen II to the screenI3 to allow for the increased transverse: deflection of .the beam as itapproaches the fluorescent screen. Thus, the aperture at the centre ofthe screen II may comprise a small circular hole I4 since there is nodeflection ofthe. beam at this point, and conveniently this hole may beformed in the cup-shaped metallic member I5 which is welded to a largeraperture in the centre of the screen I Ix as shown in Fig... 1whichmember I5 constitutes they final accelerating anode.

The aperture I6 in the screen I2 may likewise be formed.. in. acup-shaped member I1 welded in a` larger aperturey inthe centre of thescreen I2T the aperture lr6 having a width in the directionperpendicular .to the plane of the drawing which is slightly greaterthan the distance between` the ends. of the pair of deecting plates `6`which lie adjacent tothe aperture I6A so as to allow for themaximumdeection4 oi the beam effected. by this pair of plates The widthof the aperture in the direction of the plane of the drawing may besmaller since the defiecting plates 6`- do not deflect. the beam in thisplane, this dimension being preferably slightly smaller thanI thedistancel between the endsof the pair of deflecting. plates 1 which areadjacent to. this aperture.v The-aperture I8 in the screen I3 is madelarger stillrk being. of a size in the. direction. of the plane of the.drawing slightly larger than. the distance between the ends of the pairof deflecting plates 1 which areadjacent the screen I3 and in. thedirection perpendicular to the plane ofv the drawing of still largersize. toallow forthe deection` which the. beam may have suffered by theaction of the plates. 6. Fig. 2 shows the arrangement of the aperturesinthe screens. A

The outer peripheries of the screens I I, I2 and- I3 are provided withflanges so that they may be welded to the cylindrical shielding metalcyl.- inder I0 within. which they are arranged in closely fittingcontact. The leads from the pairs of deecting plates, shownat I9 and 20in the caseof the plates (1,. pass through. insulating sleeves 2| and 22to the external contactsf23, 24, apertures 25, 26 being provided in themetal shielding cylinder I'to aIl-owthe leads and insulating sleeves topasstherethrough. 'Ihe leads (not shown) from the deflecting plates 6are similarlyconnected through .insulating sleeves and appropriatelypositioned apertures inthe shielding"cylind`er Ill to theircorresponding external contacts 21, 28. y

Also passing through the screening assembly are fourv main stay-wires29- which are welded to-portions of the screens II, l2y and I3 struck upfrom apertures 3U therein-through which the wires pass. These wiresterminate Vat the screen I3 but extend beyond the screenv I I, theirends being welded .to eyelets 3l secured in apertures in a -mica disc 32which supports onelendy of the cathode ray gun structure.V The other epdof the cathode gun structure is similarly supported by a mica disc 33having apertures therein corresponding to the positions of the main staywires 29, which apertures are fitted with eyelets 34 which are alsowelded to the stay wiresr In this way, the. cathode gun structure may-Ybe easily assembled in correct alignment with the apertures in thescreens I I, I2 and I3.

The deflecting plates 6 and 1 are also supported by and located relativeto the main stay wires- 29 by being insulatingly supported therefrom bymeans of mica discs at opposite ends of. eachy compartment, the micadiscs having apertures which rit-closely to the main stay wires and;between which are supported further wires which carry ,the deectingplates. In the case of: the' deflecting plates 6, mica discs 35, 36 arearranged' at opposite ends of the compartment enclosing these deectingplates which discs have apertures through which the stay wires 29 passand; prevent rotation of the discs relative to the stay' Wires. Mountedbetweenand` welded to the eyeletsy 3-1, 38 secured in the discs 35 and36. respectively are twoy pairsl of stout wires- 39, each pair of whichare bridged by a further pair of stout wires 4Ilto each of which areattached opposite, ends of one ofthe deflecting plates Similarly, inthecase of the deflectingr plates- 1, these are supported by two mica discs4I, 42

arranged at. opposite ends of the compartment.

enclosing thev plates 1 and apertured to fity the:

stay wires-29,. the plates 1 being supported-by two, pairs oflongitudinal stout wires- 43 welded. to

eyelets44-,- 45 secured respectively to the mica discs 4I and 42.,each-pair of longitudinal wires 43 being bridged by a pairof transversewires 46 to which opposite ends` ofY the deflecting plates 1. arewelded.l

It will be appreciated. that, with the method of construction described,the cathode gun, the apertures in. the. partitioning screens and thedeflecting plates are all located relative tothe main stay wires 29 and.can. be easily assembled outside the tube envelope in correct align-mentand spacial. relationship..

In order to4 ensure insulation between the .ends of-the eyelets 31, 38,44 and 45 and the adjacent portions of the partitioning screens I I, IZand I3, the screens may be formed with recesses 41 opposite the ends ofthe eyelets so as to provide. additional clearance between the eyeletsand the screens. Such a recess is shown at 4.1 in screen I2.. Similarrecesses may .be provided as shown at.41' and. 4-1 in theV case ofscreens I I and I3 but asan alternative or additional measure, thedrawing shows a further mica disc y48 disposed between the screen II andthe ends of the eyelets 31 to ensure this insulation.y This mica dischas no apertures which willY allow the eyelets 31 to contact the screenII. The drawing shows similar insulating mica discs at 49 and 50. forrespectively insulating the ends ofthe eyelets 44 and 45 from thescreens I2 and I3, A11 these additional insulating. mica discs areperforated to register with the main stay wires 29.

'The metal shielding Cylinder I0 preferably' closely lits the intern-alsurface of the neck. portion I ofthe tube envelope so that it servesaccurately to locate the entire assembly within the neck portion of thetube. The remaining part of the tube. between the neck and extendingalmost up to the fluorescent screen may be screened in known manner bycoating the internal surface thereof with graphite 50 which may beelectrically connected to the screening assembly I0,

Il, l2 and I3 by means of the contact spring 5|.

The lead 52 to the final anode and the screening assembly may be takenout through the stem of the tube.

Figs. 1 and 2 show an arrangement in which the two pairs of deflectingplates are respectively connected to external contacts arranged at rightangles to each other. Fig. 3 shows a slightly modified arrangement inwhich the external contacts to both sets of plates are brought out inthe same plane. IIhis facilitates mounting the tube on the chassis onwhich the circuit components are assembled and permits shorter leadsfrom the output valves connected to the deflecting plate leads. Fig. 3also shows an additional external contact 53 which provides anadditional short connection to the shielding cylinder I to provide aneffective earth connection to the internal shielding arrangement. A leadto the shielding arrangement, which also constitutes the linal anode, isalso brought out through the tube stem asA shown in Fig. 1 in order tofacilitate wiring connection of the static tube circuits.

Owing to its high deflection sensitivity the tube should be carefullyshielded by earthed mu-metal shields. The screening between the twodeecting plate systems can be further increased by providing a wellfitting earthed externalscreen 54 between the leads to the two sets ofdeiiecting plates.V

An alternative method of assembly which has been found useful in manycases is to form the sets of deflecting plates into packets, each packetbeing constituted by a pair of deflecting plates with ilexible leadwires attached to them, and mounted on a pair of suitably shaped micadiscs, the planes of which extend perpendicularly to the axis of thetube. One of the shielding partitions may be Vfixed to one of the micadiscs. The packets may then be combined into` a single long packet byjoining the individual packets together, for instance by eyeleting thetop mica disc of one packet to the shielding partition xed to the bottommica disc of the succeeding packetj The complete long packet, having thedeflecting plates and shielding partitions in their proper relativepositions, is then inserted into the shielding cylinder, care beingtaken to thread the flexible plate leads through the appropriate holesin the mantle of the shielding cylinder, and is nally secured by weldingthe bottom shield, forming the final anode, to the shielding cylinder,the internal partitions making contact with the shielding cylinder. Thecomplete assembly is then lxed to the other parts of the electron gunstructure by means of insulated wires, clamps or beads in a known way.

The described methods of assembly, which form part of the invention,combine the advantages of the low capacity of deflecting plates havingleads sealed through the sides of the glass envelope with a precise jigassembly, which was hitherto only possible if the entire electrodestructure were mounted on a common stem.

I claim: y a

1. In a cathode ray tube, an electrostatically shielded beam deiiectingstructure comprising a plurality of deeoting plate units assembled inend to end relation, each unit including spaced insulating supportsdisposedv transversely of the unit at opposite ends thereof, a pair of`dei'lecting plates extending longitudinally of the unit between saidsupports, and means for supporting said plates from said supports, ametallic shielding tube embracing said assembly to enclose said unitstherewithin, and transverse metallic shielding means partitioning saidtube into compartments each containing one of said units, whereby thepairs of deflecting plates ofsaid units are electrostatically shieldedfrom each other, said partitioning screening means and said supportshaving aligned apertures therein to permit an electron beam to passtherethrough.

2. In a cathode ray tube, an electrostatically shielded beam defiectingstructure comprising a plurality of deliecting plate units assembled inend to end relation, each unit including spaced insulatingv supportsdisposed `transversely of the unit at opposite ends thereof, a pair ofdeflecting plates extending longitudinally of the unit betweensaidsupports, and means for supporting said plates from said supports, ametallic shielding tube embracing said assembly to enclose said units'therewithin, and a plurality of transverse metallic screensincluding ascreen between each of said units and a screen at each'end of saidassembly to partition said' tube into metallic Walled compartments eachcontaining one of said units, whereby the pairs of deflecting platescomprised in said units are electrostatically shielded from one another,said partitioning screens and said supports having aligned aperturestherein to allow an electron lbeam to pass therethrough,

3. A cathode ray tube comprising a vessel having an electron responsivesurface at one end thereof, an electron gun structure at the other endthereof forprojecting a beam of electrons towards said surface, and abeam deecting structure between said gun structure and said surface,`

i said beam deilecting structure comprising a plu` rality of deflectingplate units assembled in end to end relation, each unit including spacedinsulating supports disposed transversely of the unit at opposite endsthereof, a pair of deflecting plates extending longitudinally of theunit between said supports, and means for supporting said plates fromsaid supports, a metallic shielding tube embracingsaid assembly toenclose said units therewithin, and a plurality of transverse metallicscreens including a screen between each of said units and a screen atthe end of said assembly which faces said gun structure to partitionsaid tube into metallic walled compartments each containing one of saidunits, wherebythe pairs of deflecting plates comprised in said units areelectrostatically shielded from one another, said partitioning screensand said supports having aligned apertures therein to allow an electronbeam produced by said gun structure to pass 1 therethrough, and saidpartitioning screen at the end 'of said assembly which faces said gunstructure constituting a nal accelerating anode of said gun structure.

4. A cathode ray tube comprising a vessel having a neck portionconnected to a bulb portion, an electron responsive surface in said bulbportion, an electron gun structure in said neck portion for projecting abeam of electrons towards said surface; and a beam deflectingstructuredisposed longitudinally in said neck portion between said gun `structureand said surface, said beam deflectingstructure comprising a `pluralityof defleeting plate units assembled in end to end relationlongitudinallyin said neck portions, each unit including spaced insulating supportsdisposed transversely of the unit at opposite ends thereof, a pair ofdeflecting plates extending longirtudinally of the unit between saidsupports, and means for supporting said plates from said supports, ametallic shielding tube embracing said assembly to ,enclose said unitstherewithin, .and transverse metallic shielding means partitioning saidtube into .compartments each containing one of said units, whereby thepairs of deflecting plates .comprised in said units areelectrostatically shielded from one another, said partitioning screeningmeans and saidsupports having aligned apertures therein to permit anelectron beam produced -by said gun structure to pass therethrough, andsaid shielding tube engaging the Wall of said neck portion to therebylocate said beam `deflecting structure in said neck portion.

5. A unitary beam-deflecting electrode structure for a cathode ray tube,.comprising a plurali-ty of structurally independent deflecting plateunits each of which includes a pair of deecting plates mounted betweenand supported from a pair of insulating plates disposed transversely atopposite ends of the unit, said units being assembled end to endValternately with transversely disposed metallic screening plates, meansxing said units and screening plates in assembled relation. and atubular metallic shield fitted on said assembly and aiiixed thereto,said shield enclosing said units therewithin and said screening platesperipherally engaging said shield to partition said shield intocompartments each containing one of said units, whereby to shield thepairs of deflecting plates comprised in said units from one another,said screening plates and said insulating plates having alignedapertures therein to permit an electron beam to pass therethrough.

6. A unitary beam-deilecting electrode structure for a cathode ray tube,comprising a plurality of structurally independent defiecting plateunits each of which includes a pair of deilecting plates mounted betweenand supported from a pair of insulating plates disposed transversely atopposite ends of the unit, said units being assembled end to endalternately with transversely disposed metallic screening plates, aplurality of stay Wires extending through said insulating plates andsaid screening plates to support said units and screening plates inaligned assembly, means xing said assembly to said stay Wires, and atubular metallic shield tted on said assembly and affixed thereto, saidshield enclosing said units therewithin and said screening platesperipherally engaging said shield to partition said shield intocompartments each containing one of said units, whereby to shield thepairs of deflecting plates comprised in said units from one another,said screening plates and said insulating plates khaving alignedapertures therein to permit an electron beam to pass therethrough.

'7. A unitary electrode structure as defined in claim 6, wherein saidscreening plates are conductively xed to said stay wires and saidtubular shield is conductively fixed to said screening plates. Y l

8. A unitary beam-deecting electrode structure for a cathode ray tube,comprising a plurality of structurally independent deecting plate unitseach of which includes a pair of deiiecting plates mounted between andsupported from a pair of insulating plates disposed transversely atopposite ends of the unit, said units being assembled end to endalternately with transversely disposed metallic screening platesincluding a plate at each end of the assembly, a plurality of parallelspaced stay wires extending through said insulating plates and saidscreening plates to support said units and screening plates in alignedassembly, said screening plates being conductively xed to said staywires, and a tubular metallic `shield extending the .full length of saidassembly being fitted therearound in engagement with the peripheries ofsaid screening plates and conductively iixed thereto, whereby saidscreening plates partition said shield into shielded compartmentscontaining said units individually, said screening plates and saidinsulating plates having aligned apertures therein to allow an electronbeam to pass therethrough.

9. A unitary electrode assembly for a cathode ray tube, comprising anelectron gun structure for producing a beam of electrons, and a unitarybeam-deiiecting structure comprising a plurality of structurallyindependent deflecting plate units each of which includes a pair ofdellecting plates mounted between and supported from a pair ofinsulating plates disposed transversely at opposite ends of the unit,said units being assembled end to end alternately with transverselydisposed metallic screening plates, a plurality of stay wires extendingthrough said insulating plates and said screening plates to support saidunits and screening plates in aligned assembly, means fixing saidassembly to said stay Wires, and a tubular metallic shield tted on saidassembly and afiixed thereto, said shield enclosing said unitstherewithin and said screening plates peripherally engaging said shieldto partition said shield into compartments each containing one of saidunits, whereby to shield the pairs of deflecting plates comprised insaid units from one another, said screening plates and said insulatingplates having aligned apertures therein to permit an electron beam topass therethrough, said stay wires having extensions projecting from theend of the beam deilecting structure which faces said gun structure, andmeans supporting said gun structure from said extensions in alignmentwith said apertures in said screening plates and insulating plates.

10. A unitary electrode assembly as deflned in claim 9, wherein saidelectron gun structure includes av pair of axially spaced insulatingsupport plates through which said stay Wire extensions pass to supportsaid gun structure therefrom, said support plates being fixed to saidextensions.

11. A unitary electrode assembly for a cathode ray tube, comprising anelectron gun structure including a pair of axially spaced insulatingsupport discs disposed perpendicular to the axis of said structure; aplurality of beam deflecting units each comprising a pair of axiallyspaced insulating support discs at opposite ends of the unit, supportmembers extending between and xed to said discs to hold said discs inspaced relation, and a pair of deflecting plates disposed between saiddiscs and supported by said support members in insulated relation toeach other; a plurality of peripherally flanged metallic shieldingdiscs; said gun structure, units, and shielding discs being assembled inaxially aligned relation with said gun structure and said units disposedend to end in succession and said shielding discs disposed one at eachend of the succession of units and between the end insulating supportdiscs of adjacent units, said shielding discs and said support discs ofboth said gun structure and said units all having locating holessimilarly posiltioned therein, a plurality of stay wires extendingparallel through said locating holes in said shielding and support discsto thereby support the assembly in axially aligned relation, means xingsaid support discs of said gun structure to said stay Wires, meansconductively nxing said shielding discs to said stay Wires, and ametallic shielding cylinder fitted on saidassembly and extending thefull length of said succession of units, said cylinderengaging theperipheral flanges of said shielding discs and being conductively fixedthereto, whereby said shielding discs partition said cylinderintoshielded compartments containing said units individually, saidshielding discs and said support discs of said units having aperturesthereingin` alignment withsaid gun structure to permit anelectronv beamproduced by said gun to pass.` therethrough, Vsaidcylinder havingapertures therein Opposite the respective compartments thereof, andlead-in conductors extending through said apertures and connected tothe` pairs of deflecting plates in the respective compartments.

12. A cathode ray tube comprising an envelope enclosing an electrodeassembly mounted therein, said assembly including a beam deflectingstructure comprising a plurality of deiiecting plate units assembled inend to end relation, each unit including spaced insulating supportsdisposed transversely of the unit at opposite ends thereof, a pair ofdeflecting plates extending longitudinally of the unit between saidsupports, and means for supporting said plates from said supports, ametallic shielding tube embracing said assembly to enclose said unitstherewithin, and transverse metallic shielding means partitioning saidtube into compartments each containing one of said units, whereby thepairs of deflecting plates of said units are electrostatically shieldedfrom each other, said partitioning screening means and said supportshaving aligned apertures therein to permit an electron beam to passtherethrough, said shielding tube having apertures in the wall thereofopposite the respective compartments thereof, and lead-in conductorsconnected to the pairs of deflecting plates in the respectivecompartments extending respectively through said apertures in said tubeand being sealed through said envelope at points adjacent the respectivepositions of s said apertures.

13. A cathode ray tube as defined in claim 12, and further comprisingexternal metallic shielding means around said envelope and extendingbetween the lead-in conductors of the respective pairs of deilectingplates.

14. A cathode ray tube as defined in claim 12, wherein said unitsinclude at least two pairs of deiiecting plates adapted for beamdeflection in different planes, and the lead-in conductors connected tothe plates of said repairs are sealed through said envelope at points'insubstantially the same plane.

15. A cathode ray tube comprising a vessel containing an electrodeassembly including an electron gun for producing a beam of electrons,and a beam deiiecting structure mounted in alignment with said gun, saiddeilecting structure comprising a plurality of structurally independentdeflecting plate units each of which includes a pair of deflectingplates mounted between and supported from a pair of insulating platesdisposed transversely at opposite ends of the unit, said units beingassembled end to end alternately with transversely disposed metallicscreening plates including a plate at each end of the assembly, aplurality of parallel spaced stay wires extending through saidinsulating plates and said screening plates to support said units andscreening plates in aligned assembly, said screening plates beingconductively iixed to said stay wires, and a tubular metallic shieldextending the full lengthof said assembly being tted therearound inengagement with the peripheriesof said. screening plates andvconductively fixed. thereto. v,whereby said screening plates partitionsaid shield into shielded compartments containing said unitsindividually, said screening plates and said insulating plates havingapertures thereinin alignment with said gun ,toallow an electron beamproduced by said gun toV pass therethrough, and the said` one of saidscreening plates at the end. of said unit assembly Awhich facesV saidgun constituting a xed anode of said gun.

161A cathode` ray `tube comprising a vessel having an electronresponsive surface at one end thereof, an electron gun at the other endthereof for projecting a beam of electrons towards said surface, and abeam deflecting structure between said gun and said surface mounted inalignment with said gun, said deflecting structure comprising aplurality of structurally independent deiiecting plate units each ofwhich includes a pair, of deflecting plates mounted between andsupported from a pair of insulating plates disposed transversely atopposite ends of the unit, said units being assembled end to en dalternately with transversely disposed metallic screening platesincluding a plate at each end of the assembly, a plurality of parallelspaced stay wires extending through said insulating plates and saidscreening plates to support said units and screening plates in alignedassembly, said screening plates being conductively xed to said staywires, and a tubular metallic shield extending the full length of saidassembly being fitted therearound in engagement with the peripheries ofsaid screening plates and conductively fixed thereto, whereby saidscreening plates partition said shield into shielded compartmentscontaining said units individually, said screening plates and saidinsulating plates having apertures therein in alignment with said gun toallow an electron beam produced by said gun to pass therethrough, thesaid one of said screening plates at thel end of said unit assemblywhich faces said gun constituting a final anode of said gun, an internalconductive coating on said vessel extending from a point adacent saidtubular shield to a point adjacent said electron responsive surface, andmeans carried by said deflecting structure electrically connecting saidcoating to said shield.

17. A cathode ray tube comprising an enclosing vessel containing anelectrode assembly including an electron gun for producing a beam ofelectrons, and a beam deflecting structure mounted in alignment withsaid gun, said vessel terminating at one end in a base carrying terminalcontacts for establishing electrical connection to electrodes of saidassembly, said deflecting structure comprising a plurality ofstructurally independent deflecting plate units each of which includes apair of deflecting plates mounted between and supported from a pair ofinsulating plates disposed transversely at opposite ends of the unit,said units being assembled end to end alternately with transverselydisposed metallic screening plates including a plate at each end of theassembly, a plurality of parallel spaced stay `wires extending throughsaid insulating plates and said screening plates to support said unitsand screening plates in aligned assembly, said screening plates beingconductivelyliixed to said stay wires, and a tubular metallic shieldextending the full length of said assembly being tted therearound inengagement with the pemames GERHARD Y LJEBMANN.-

